In the food industry, as disclosed in the international application WO 00/15670, oxidized starch can be used as a thickener, for example in sauces, or to replace Arabic gum in products such as confectioneries.
It is also known to use oxidized starch as an additive for the paper industry. In this field, the purpose of adding the oxidized starch is usually to improve the strength of the paper sheet, and/or to result in a better printability of the paper sheet, and/or a better retention of cationic additives, and/or to improve its applicability as glue for the paper fibers. For instance, oxidized starches have been used as coating binders, as disclosed in the international application WO 00/15670.
The oxidation of starch is usually carried out in order to reduce the viscosity of the starch in solution or dispersion. During the oxidation reaction, starch molecules are broken down, yielding molecules having a decreased molecular weight.
The oxidation process can be carried out using an alkali metal hypochlorite or a peroxide such as hydrogen peroxide as oxidizing agent.
An example based on the use of hypochlorite as oxidant is given in the international application WO 03/018638. When hydrogen peroxide is used, the oxidation reaction is generally conducted in the presence of a catalyst such as a metal catalyst in order to shorten the reaction time. For example, WO 00/15670 discloses the use of copper catalysts. Another example is the use of manganese-based complex coordination catalysts, disclosed in U.S. Pat. No. 5,833,755.
However, the oxidized starch thus obtained is not suitable as additive for the paper industry and for the food industry. Indeed, the resulting oxidized starch usually has a too low viscosity for most of the required applications and/or the viscosity is not stable as retrogradation is observed, leading to the formation of a gel.